This invention relates to sample injection techniques and more particularly to sample injection for instruments requiring gas or vapor samples such as for example mass spectrometers or gas chromatographs.
One class of sample injector utilizes a moving medium such as a belt or conveyor that carries the samples separated in one instrument into or to another instrument. This class of sample injector is used, for example, to transfer samples from a liquid chromatograph into a mass spectrometer in real time. In these known devices, the samples are caused to adhere to the surface of the belt or conveyor by solvent evaporation and moved into the mass spectrometer where they are subjected to further analysis.
In one type of prior art sample injector of this class, a belt runs from a liquid chromatograph into the high vacuum ionization chamber of a mass spectrometer. The effluent from the outlet of the liquid chromatograph is applied to the belt where it quickly dries and, after being dried, is carried through a series of differentially pumped vacuum locks into the high vacuum ionization chamber of a mass spectrometer for analysis. The sample is then driven off the surface of the belt by heating means or particle bombardment means and ionized in the mass spectrometer source.
These prior art sample injectors have several disadvantages such as: (1) the number of samples analyzed per unit time is limited by the elution rate of a liquid chromatograph; (2) they require movement of an endless or continuous belt from a region of atmospheric pressure to a region of high vacuum; and (3) high levels of operator skill are needed to operate and maintain systems of this type. The above characteristics cause the prior art sample injector techniques to be technically complex and relatively expensive, particularly since they tie up a mass spectrometer while the liquid chromatograph, which is a much less expensive instrument, operates.